34th Solar Physics Division Meeting, June 2003
Session 26 The Changing Solar interior II
Oral, Friday, June 20, 2003, 9:00am-12:00noon, Auditorium

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[26.06] The Solar Dynamo

M. Dikpati (High Altitude Observatory, NCAR)

Cyclic evolution of solar magnetic features is believed to be due to a dynamo operating in the Sun. Recently, 2D kinematic flux-transport dynamos have been successful in explaining many large-scale solar cycle features, including the correct phase relationship between the equatorward migrating sunspot belt and the poleward drifting large-scale, diffuse fields. Flux-transport dynamos work well for the Sun because they include three basic processes; (i) generation of toroidal fields by shearing the pre-existing poloidal fields by differential rotation (the omega-effect), (ii) re-generation of poloidal fields by lifting and twisting the toroidal fluxtubes (the alpha-effect) and (iii) an essential third process -- flux transport by meridional circulation. Earlier models included only the first two of these. Dynamo cycle period is primarily governed by meridional flow speed in this class of models. The meridional flow plays a key role in governing the Sun's memory about its own magnetic field -- the slower the flow, the longer the memory. Reviewing these successes, we will present new model calculations to show how this memory-effect can influence the upcoming cycle's strength and duration, often causing peculiar features. For example, cycle 23 never reached an average odd-cycle's strength and suddenly showed a second maximum during its declining phase. We will close by discussing our on-going efforts for building a 3D flux-transport dynamo that could explain longitude-dependent solar-cycle features, such as, "active longitudes". We acknowledge support from NASA through awards W-19752, W-10107 and W-10175. National Center for Atmospheric Research is sponsored by National Science Foundation.

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Bulletin of the American Astronomical Society, 35 #3
© 2003. The American Astronomical Soceity.